By default, all the sections will be collapsed. To set a section to be open when the page loads, add the data-collapsed="false" attribute to the heading of the section you want expanded.

Should read "The last section will be open by default."actually, it's the last section where data-collapsed hasn't been setie, if there are 3 sections and data-collapsed=true on the 3rd, the 2nd section will now be open by default

The only way to have all sections collapsed is to explicitly set data-collapsed="true" to all sections